In the electrostatic printing and plotting, or imaging, arts, various systems have been developed over the years in which a latent image first is electrostatically imparted to a moving record medium and then is developed or toned by the application of a toning material which adheres to the electrostatically produced latent image. Both dry and liquid toners have been used and each has been found to have its own peculiar characteristics, advantages and problems.
Of particular interest with regard to the present application are those systems in which liquid toners are used.
Typically in liquid toned electrostatic systems, an excess of toner is applied to the record medium to ensure adequate development; then the excess is drawn away by some means and the record medium is allowed to dry. U.S. Pat. No. 3,654,659, issued to John Blumenthal, the present applicant, and also assigned to the assignee of the present application, discloses a type of liquid toner clean-off system for high speed operation. The wet record medium is drawn past an elongated suction opening which is just upstream of a narrow land lying in the same plane as the suction opening. Air is drawn over the land when suction is applied to the suction opening, thereby skimming excess toner from the record medium. While this technique has achieved a significant measure of success, the flat configuration of the clean-off head makes effective sealing with the record medium difficult, thereby requiring the use of rather high vacuum, as in the case of the toning head previously mentioned.
Those skilled in the art will appreciate that a need has existed for some time for a reliable toner clean-off head which will not rely on the use of high vacuum to ensure proper engagement between the head and the record medium. The present invention seeks to satisfy these needs.